5.3.2.5 Case Study 3: Ratios between platter forms Drag. 15/17 and 18

The platter or plate forms Drag. 15/17 and 18 are familiar forms of the middle and later first century AD. They were contemporary, but through the latter half of the first century the 15/17 is known to become less frequent amongst assemblages while the 18 remains a prominent form. Millett notes that the ratio of these two La Graufesenque forms at Cirencester, in the well known fort ditch deposit of c. AD 55-65, is 1:1 (Millett 1993b; Wacher and McWhirr 1982; though it might be relevant to bear in mind that this could be a structured deposit (cf. Willis 1997a)), while at Fishbourne c. AD 70 the ratio is 1 15/17 to 4.4 Drag. 18s. To take these two samples in order, in the case of the early and middle Neronian period, the database assembled for this project (see Tables 80 and especially Table 81) suggests that generally at this time the Drag. 18 is 30% more common than the 15/17, with ratios of c. 1:1.3. The database assembled for this project (Table 80 and Table 81) shows, though, that at around AD 70 the Drag. 18 is approximately 4 times more frequent than the Drag. 15/17, and thus there is agreement in this case with the Fishbourne sample (compare SGLG 15/17 with SGLG 18). Data on the relative frequency of these two platter forms at the fort at Zwammerdam, c. AD 47-69, is consistent with the evidence in the database (Haalebos 1977). This relative decline in the frequency of 15/17 compared to the form 18 was noted by Jo Groves in her study of the pottery from Leadenhall Court, London (1993, 126). Hence the ratio of form 15/17 to form 18 is likely to be a good indicator of the approximate date of a group in the second half of the first century.

5.3.2.6 Case Study 4: Ratios between Drag. 18/31 or 18/31R dishes and Drag. 31 (dish) or 31R (bowl) in the second century

These types are, potentially, further good chronological indicators as they were evidently successive (cf. Webster 1996). The 18/31 dates principally to the period c. AD 100-150, the 31 to c. AD 150-200+; likewise the 18/31R dates from c. AD 100 to 160, the 31R from c. AD 160-200+. The relative proportions of these forms within second century groups are likely therefore to represent a chronological index for that era.

Dickinson examined the relative frequency of these types amongst the assemblage from Ribchester 1980/1989-90, and ascertained that the ratios of forms 18/31 to 31 and 18/31R to 31R were 28:20 and 6:1. This was taken to indicate an emphasis amongst the assemblage on the Hadrianic and early Antonine periods (Dickinson 2000a, 204; see Table 4). In this case, in itself, this samian information might mean that there was lower intensity of occupation during the period associated with the Drag. 31 and 31R (ie. from c. AD 150/160), or that occupation ceased at some time not long after c. AD 160.

Similarly, in her examination of the samian from Alchester, 1991, Dickinson presented data on the ratios of forms 18/31 to 31 at Sites B and C drawing on the assemblage as a whole (not by phase). The ratios were 18/31 to 31, 1:6.6 at Site B, and 1:3.75 at C (Dickinson 2001d). Dickinson states that the emphasis of the site collection is therefore on: "the second half of the 2nd century" (2001d, 277-8). (In this case no data of this kind is presented by phase). The database assembled for this project (cf. Table 80 and Table 81) suggests that this order of difference in the frequency of the forms begins c. AD 175 which tallies with Dickinson's observation.

5.3.2.7 Evaluation of the method

The composition of pottery groups by form can, of course, be a dating index. This project has aimed to establish the character of ratios between individual samian form types as a guide to assist dating. In effect the database produces a 'master-index' for the relative frequency of samian form types within archaeological deposits over time. This can be used as an index for dating site groups. Some 'good indicators', in terms of specific forms, such as the cups Drag. 27 and 33 were examined and shown to have clear trends which may be used as an index for dating. The case study examples demonstrate the utility of the method. Other pairs of forms/types may be a useful guide (eg. Drag. 24/25 to 27 for the first century AD). The data assembled are also presented via the ADS archive for downloading so that the non-specialist can extract specific types by year or years and compare their own groups with the form ratios of the database, thus providing a guide towards a confident 'close' date for recovered samian groups which can be fed into the chronological framework of archaeological projects. This method thereby represents a supplementary means of dating samian.